Genetic modification of hematopoietic stem cells (HSC) the potential of reconstituting immune function in HIV-infected with a lifelong source of hematopoietic cells resistant to HIV infection. However, retroviral vectors based on Moloney murine leukemia virus have proved to be relatively inefficient in transducing primate HSC, in large part due to the inability of these vectors to transduce quiescent cells. Construction of retroviral vectors based on lentiviral vectors has resulted in efficient transduction of many quiescent cell types, including hematopoietic progenitor cells, and suggests that these vectors may efficiently transduce HSC. However, demonstration of the efficacy and safety of these vectors for HSC gene therapy will require in vivo studies. Recent collaborative work between our laboratory and Dr. Wong-Staal's laboratory has demonstrated that introduction of an SIV-specific ribozyme into rhesus CD34+ hematopoietic cells can induce a relatively high level of resistance to SIV infection in both CD4+ T cells and macrophages derived from these cells. The objective of this proposal is to examine the ability of HIV and FIV- based vectors encoding an SIV-specific ribozyme to transduce HSC and to protect hematopoietic progeny from SIV infection both in vitro and in vivo. Specific aims include: 1. To assess the ability of HIV and FIV vectors encoding an SIV-specific ribozyme to transduce rhesus hematopoietic progenitor cells in vitro and to inhibit SIV replication in their progeny; 2. To examine the ability of lentivirus-based vectors to transduce HSC in normal macaques; and 3. To examine the ability of HSC transduced with lentivirus vectors encoding an SIV-specific ribozyme to protect hematopoietic cells from SIV infection in vivo. 4: To determine the potential mobilization and pathogenicity of HIV and FIV vectors in rhesus macaques in vivo. These studies should yield important information regarding the efficacy and safety of lentivirus vectors for stem cell gene therapy for AIDS.